I can only talk about the Netherlands: Round white sign with a red band, black letters: maximum speed Square blue sign with white letters, advisory speed (advisory speed < maximum speed - 20 )

There is no minimum speed (round blue sign white letters): this is for the simple reason you could technically be ticketed in the case of a traffic jam, yield sign or traffic light

0118 999 881 999 119 725 - 3

Just finished the first season of The Wire